Capping Layer for Improved Deposition Selectivity

ABSTRACT

The present disclosure relates to a method and apparatus for improving back-end-of-the-line (BEOL) reliability. In some embodiments, the method forms an extreme low-k (ELK) dielectric layer having one or more metal layer structures over a semiconductor substrate. A first capping layer is formed over the ELK dielectric layer at a position between the one or more metal layer structures. A second capping layer is then deposited over the one or more metal layer structures at a position that is separated from the ELK dielectric layer by the first capping layer. The first capping layer has a high selectivity that limits interaction between the second capping layer and the ELK dielectric layer, reducing diffusion of the atoms from the second capping layer to the ELK dielectric layer and improving dielectric breakdown of the ELK dielectric layer.

BACKGROUND

The fabrication of integrated chips can be broadly separated into twomain sections, front-end-of-the-line (FEOL) fabrication andback-end-of-the-line (BEOL) fabrication. FEOL fabrication includes theformation of devices (e.g., transistors, capacitors, resistors, etc.)within a semiconductor substrate. BEOL fabrication includes theformation of one or more metal interconnect layers comprised within oneor more insulating dielectric layers disposed over the semiconductorsubstrate. The metal interconnect layers of the BEOL electricallyconnect individual devices of the FEOL to external pins of an integratedchip.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B illustrate cross-sectional views showing formation of aback-end-of-the-line metal layer using a conventional metal cappingprocess.

FIG. 2 is a flow diagram of some embodiments of a disclosed method ofintegrated chip processing that improves back-end-of-the-linereliability.

FIG. 3 a cross-sectional view of some embodiments of aback-end-of-the-line (BEOL) layer comprising a first capping layerconfigured to improve BEOL reliability.

FIG. 4 illustrates graphs showing exemplary cobalt selectivity achievedby a disclosed first capping layer comprising an extreme low-k (ELK)film.

FIG. 5 is a flow diagram of some embodiments of a method of integratedchip processing that improves back-end-of-the-line (BEOL) reliability.

FIGS. 6-13 illustrate cross-sectional views of some embodiments of anintegrated chip (IC) whereon a disclosed method of integrated chipprocessing that improves back-end-of-the-line reliability isimplemented.

DETAILED DESCRIPTION

The description herein is made with reference to the drawings, whereinlike reference numerals are generally utilized to refer to like elementsthroughout, and wherein the various structures are not necessarily drawnto scale. In the following description, for purposes of explanation,numerous specific details are set forth in order to facilitateunderstanding. It will be appreciated that the details of the figuresare not intended to limit the disclosure, but rather are non-limitingembodiments. For example, it may be evident, however, to one of ordinaryskill in the art, that one or more aspects described herein may bepracticed with a lesser degree of these specific details. In otherinstances, known structures and devices are shown in block diagram formto facilitate understanding.

FIGS. 1A-1B illustrates cross-sectional views, 100 and 108, showingformation of a back-end-of-the-line (BEOL) metal layer of an integratedchip (IC) using a conventional metal capping process.

As shown in cross-sectional view 100, a low-k dielectric layer 104 isformed over a semiconductor substrate 102. One or more metal layerstructures 106 are formed within the low-k dielectric layer 104. Asshown in cross-sectional view 108, after formation of the metal layerstructures 106, a capping layer 110 (e.g., a cobalt capping layer)having a substantially uniform thickness is deposited over the low-kdielectric layer 104 and the metal layer structures 106. The cappinglayer 110 improves electromigration at the top interface of metal layerstructures 106. An etch stop layer 112 may be subsequently depositedover the capping layer 110 prior to the formation of an overlying metallayer.

In modern technology nodes (e.g., 45 nm, 32 nm, 22 nm, 14 nm, etc.),low-k dielectric layers, having a low dielectric constant, are used toprovide good electrical isolation between adjacent metal layerstructures, allowing for spaces between adjacent metal layer structuresto shrink and the density of an integrated chip to increase. However,low-k dielectric layers often have a high porosity. The high porosity oflow-k dielectric layers leads to diffusion of atoms from the cappinglayer 110 into the underlying low-k dielectric layer 104. Such diffusionlead to reliability issues, such as poor time dependent dielectricbreakdown (TDDB) and voltage breakdown (VBD).

Accordingly, the present disclosure relates to a method and apparatusfor improving back-end-of-the-line (BEOL) reliability. In someembodiments, the method comprises forming an extreme low-k (ELK)dielectric layer comprising one or more metal layer structures over asemiconductor substrate. A first capping layer is deposited over the ELKdielectric layer at a position between the one or more metal layerstructures, resulting in a planar surface having metal layer structuresinterspersed between the first capping layer. A second capping layer isthen deposited over the one or more metal layer structures. The firstcapping layer has a high selectivity that limits interaction between thesecond capping layer and the ELK dielectric layer, reducing diffusion ofthe atoms from the second capping layer to the ELK dielectric layer andimproving dielectric breakdown of the ELK dielectric layer.

FIG. 2 is a flow diagram of some embodiments of a method 200 ofintegrated chip processing that improves back-end-of-the-line (BEOL)reliability by reducing BEOL time dependent dielectric breakdown (TDDB)and voltage breakdown (VBD) caused by diffusion from a first cappinglayer into a dielectric material.

At act 202, a low-k dielectric layer is formed over a semiconductorsubstrate. In some embodiments, the low-k dielectric layer comprises anextreme low-k (ELK) dielectric layer with a high porosity having adielectric constant in a range of between approximately 2.4 and 2.6 anda density in a range of between approximately 1.08 g/cm³ toapproximately 1.15 g/cm³.

At act 204, a first capping layer is deposited over the low-k dielectriclayer. In some embodiments the high density first capping layer has adensity greater than that of the underlying low-k dielectric layer. Thefirst capping layer may be deposited by a blanket deposition of a highdensity ELK film or a non-porous non-ELK film. In some embodiments, thehigh density ELK film comprises an ELK film (e.g., SiCO) having adielectric constant in a range of between approximately 2.6 and 2.8. Inother embodiments, the non-ELK film may comprise silicon nitride (SiN),silicon oxide (SiO), silicon carbon nitride (SiCN), or another similarmaterial.

At act 206, a metal layer extending though the first capping layer isformed within the low-k dielectric layer. The resulting structure formsa substantially planar top surface of the substrate having exposed metallayer structures interspersed between the first capping layer.

At act 208, a second capping layer is selectively deposited. Surfaceproperties of the first capping layer cause for the second capping layerto selectively accumulate to a greater thickness over the metal layerstructures relative to the first capping layer, thereby providing for ahigh selectivity of between the first capping layer and the metal layerstructures. For example, in some embodiments, the thickness of thesecond capping layer over the metal layer structures is greater than tentimes the thickness of the second capping layer over the first cappinglayer. In some embodiments, the second capping layer may comprisecobalt.

Therefore, method 200 deposits a first capping layer that minimizesinteractions between the second capping layer and the underlying low-kdielectric layer. By minimizing interactions between the second cappinglayer and the underlying low-k dielectric layer, diffusion from thesecond capping layer to the underlying porous dielectric material ismitigated, improving TDDB and VDB reliability.

FIG. 3 illustrates a cross-sectional view of some embodiments of aback-end-of-the-line (BEOL) layer 300 comprising a first capping layerconfigured to improve BEOL reliability.

As shown in BEOL layer 300, a first etch stop layer 302 is disposed overa semiconductor substrate 102. In some embodiments, the semiconductorsubstrate 102 may comprise one or more semiconductor devices. In variousembodiments, the first etch stop layer 302 may comprise silicon nitride(SiN), silicon oxide (SiO), or silicon carbon nitride (SiCN), forexample.

A low-k dielectric layer 304 is located over the first etch stop layer302. In some embodiments, the low-k dielectric layer 304 comprises anextreme low-k (ELK) dielectric layer. The ELK dielectric layer maycomprise a lower ELK dielectric layer 304 a and upper ELK dielectriclayer 304 b. The lower ELK dielectric layer 304 a comprises an interfacelayer, located between the upper ELK dielectric layer 304 b and thefirst etch stop layer 302, which has a higher density and dielectricconstant than the upper ELK dielectric layer 304 b. The lower density ofthe upper ELK dielectric layer 304 b causes the upper ELK dielectriclayer 304 b to comprise a porous material having a low dielectricconstant, k. In some embodiments, the upper ELK dielectric layer 304 bcomprises a density in a range of between approximately 1.08 g/cm³ andapproximately 1.15 g/cm³, which provides for a dielectric constant in arange of between approximately 2.4 and approximately 2.6.

A first metal layer 306 is disposed within the low-k dielectric layer304. In various embodiments, the first metal layer 306 may comprise ametal interconnect layer 306 a and/or a metal via layer 306 b (i.e., ametal contact layer). Although FIG. 3 illustrates metal layer 306 ascomprising both metal interconnect layers 306 a and metal via layers 306b, it will be appreciated that a metal layer may comprise one or morethe other, but not necessarily both. In some embodiments, the firstmetal layer 306 comprises a copper metal layer.

A first capping layer 308 is formed over the low-k dielectric layer 304at a position between structures of the metal layer 306, resulting instructures of the first metal layer 306 being interspersed between thefirst capping layer 308 along a planar interface 310. In someembodiments, the first capping layer 308 may comprise a non-ELK film. Insome embodiments, the first capping layer 308 may comprise a siliconnitride (SiN) film having a density of greater than 2.4 g/cm³. In otherembodiments, the first capping layer 308 may comprise a silicon carbonnitride (SiCN) film having a density in a range of between approximately1.5 g/cm³ to approximately 2.0 g/cm³. In yet other embodiments, asilicon dioxide (SiO₂) film having a density of approximately 1.5 g/cm³.

In other embodiments, the first capping layer 308 may comprise an ELKfilm having a density that is greater than a density of the underlyinglow-k dielectric layer 304 (e.g., the upper ELK dielectric layer 304 b).For example, in some embodiments, the first capping layer 308 maycomprise a silicon oxycarbide (SiCO) film having a density in a range ofbetween approximately 1.3 g/cm³ and approximately 1.4 g/cm³. Suchdensities provide for a dielectric constant having a value in a range ofbetween approximately 2.8 and approximately 3.0. The higher density ofthe ELK film provides for a lower porosity than that of the underlyingupper ELK dielectric layer 304 b.

A second capping layer 312 is disposed over the first metal layer 306.The first capping layer 308 has surface properties that improveselectivity of the second capping layer 312 between the first metallayer 306 and the first capping layer 308, so that the second cappinglayer 312 forms to a greater thickness over the first metal layer 306than over the first capping layer 308. Improving the selectivity of thesecond capping layer 312, reduces diffusion from the second cappinglayer 312 to the underlying low-k dielectric layer 304, therebyimproving TDDB and VDB reliability.

For example, in some embodiments, the second capping layer 312 maycomprise a cobalt capping layer configured to improve electromigrationat a grain boundary of the first metal layer 306. The first cappinglayer causes deposition of cobalt to proceed with a high selectivitythat causes cobalt to easily accumulate over a metal surface but to noteasily accumulate over the first capping layer.

In some embodiments, a second etch stop layer 314 may be disposed overthe first capping layer 308 and the second capping layer 312. The secondetch stop layer 314 has a first thickness t₁ over the first cappinglayer 308 and a second thickness t₂ over the second capping layer 312.The first thickness t₁ is greater than the second thickness t₂ (i.e.,t₁>t₂), since the second capping layer 312 has a greater thickness overthe first metal layer 306. Additional metal layers 318 may be formed inadditional dielectric layers 316 located over the second etch stop layer314, in some embodiments.

FIG. 4 illustrates a graph 400 showing exemplary cobalt selectivityprovided by surface properties of a disclosed first capping layercomprising an ELK film disposed over a blank semiconductor wafer. Asprovided herein, cobalt selectivity is the ratio of cobalt thicknessover a copper metal layer to cobalt thickness over an extreme low-k(ELK) dielectric layer.

As shown in graph 400, the selectivity a first capping layer comprisingan ELK film is directly proportional to the dielectric value of the ELKfilm. For example, an ELK film having a first dielectric value of k=2.6,corresponding to a first density, provides for a copper selectivity of314. An ELK film having a second dielectric value of k=2.8,corresponding to a second density greater than the first density,provides for a copper selectivity of 4550.

It has been appreciated that the density of an ELK film has an inverseproportionality to the porosity of the ELK film and a directproportionality to the dielectric value of the ELK film. Therefore, theselectivity a first capping layer comprising an ELK film is directlyproportional to the density of the first capping layer, such that byusing a first capping layer with a higher density (i.e., a higherdielectric constant) the selectivity of the first capping layer can beincreased.

FIG. 5 is a flow diagram of some embodiments of a method 500 ofintegrated chip processing that improves back-end-of-the-line (BEOL)reliability.

While the disclosed methods (e.g., methods 200 and 500) are illustratedand described below as a series of acts or events, it will beappreciated that the illustrated ordering of such acts or events are notto be interpreted in a limiting sense. For example, some acts may occurin different orders and/or concurrently with other acts or events apartfrom those illustrated and/or described herein. In addition, not allillustrated acts may be required to implement one or more aspects orembodiments of the description herein. Further, one or more of the actsdepicted herein may be carried out in one or more separate acts and/orphases.

At act 502, a first etch stop layer is formed over a semiconductorsubstrate.

At act 504, an extreme low-k (ELK) dielectric layer is formed over thefirst etch stop layer. In some embodiments, the ELK dielectric layer isformed by first forming a lower ELK dielectric layer having a firstdensity, and subsequently forming an upper ELK dielectric layer over thelower ELK dielectric layer. The upper ELK dielectric layer has a seconddensity that is less than the first density.

At act 506, a first capping layer is deposited over the ELK dielectriclayer. The first capping layer 308 comprises surface properties thatlimit accumulation of a second capping layer (act 516) over the firstcapping layer. In some embodiments, the first capping layer may comprisean ELK dielectric film (e.g., SiCO) having a higher density (i.e.,higher dielectric constant) than the underlying ELK dielectric layer. Inother embodiments, the first capping layer may comprise a non-ELKdielectric material, such as silicon nitride (SiN), silicon carbidenitride (SiCN), or silicon dioxide (SiO₂).

In some embodiments, the first capping layer may be deposited by way ofan “ex-situ process”, in which the first capping layer (e.g., SiN, SlCN,or SiO₂) is deposited over a porous ELK film, after deposition of theELK dielectric layer, by use of a different tool. In such embodiments,the substrate is exposed to an ambient environment between deposition ofthe ELK dielectric layer and the first capping layer. In otherembodiments, the first capping layer may be deposited by way of an“in-situ process”, in which the first capping layer (e.g., the dense ELKfilm) is deposited over an underlying ELK dielectric layer by a sametool. In such embodiments, the first capping layer is formed withoutbreaking the vacuum used to deposit the underlying ELK dielectric layer.

At act 508, a hardmask is selectively formed over the first cappinglayer. The hardmask is selectively formed to have a plurality ofopenings that expose the first capping layer at locations correspondingto one or more metal layer structures.

At act 510, the ELK dielectric layer and the first capping layer areselectively etched according to the hardmask to form a plurality ofcavities within the substrate. The plurality of cavities extend thoughthe first capping layer into the ELK dielectric layer, so that theplurality of cavities are disposed between openings in the first cappinglayer.

At act 512, a metal material is deposited over the substrate to fill theplurality of cavities.

At act 514, a chemical mechanical polishing (CMP) process is performedto remove excess metal material and the hardmask. The CMP processresults in a planar surface comprising a plurality of metal layerstructures disposed between the first capping layer.

At act 516, a second capping layer is selectively deposited over thesubstrate. In some embodiments, the second capping layer comprises acobalt layer. The high selectivity of the first capping layer causes thesecond capping layer to form to a greater thickness over the metal layerstructures than over the first capping layer. For example, in someembodiments, the second capping layer may be formed over the metal layerstructures to a thickness that is greater than ten times the thicknessof the second capping layer over the first capping layer.

At act 518, a second etch stop layer is optionally deposited over thefirst capping layer and the second capping layer, in some embodiments.The second etch stop layer has a substantially flat top surface and afirst thickness over the first capping layer and a second thickness overthe second capping layer.

It will be appreciated that method 500 may be iteratively performed toform a plurality of metal layers in a back-end-of-the-line (BEOL) stack.

FIGS. 6-13 illustrate cross-sectional views of some embodiments of anintegrated chip (IC) layout whereon a disclosed method of integratedchip processing that improves back-end-of-the-line (BEOL) reliability isimplemented.

FIG. 6 illustrates some embodiments of a cross-sectional view 600corresponding to act 502. As shown in cross-sectional view 600, a firstetch stop layer 302 is formed over a semiconductor substrate 102. Invarious embodiments, the semiconductor substrate 102 may comprise anytype of semiconductor body (e.g., silicon, SiGe, SOD such as asemiconductor wafer and/or one or more die on a wafer, as well as anyother type of metal layer, device, semiconductor and/or epitaxiallayers, etc., associated therewith. In various embodiments, the firstetch stop layer 302 may comprise a layer of silicon nitride (SiN),silicon oxide (SiO), or silicon carbon nitride (SiCN).

FIG. 7 illustrates some embodiments of a cross-sectional view 700corresponding to act 504. As shown in cross-sectional view 700, anextreme low-k (ELK) dielectric layer 304 is formed over the first etchstop layer 302. In some embodiments, the ELK dielectric layer 304 isformed by first depositing a lower ELK dielectric layer 304 a having afirst dielectric constant over the first etch stop layer 302. An upperELK dielectric layer 304 b, having a second dielectric constant lessthan the first dielectric constant, is subsequently deposited over thelower ELK layer 304 a. The lower dielectric constant of the upper ELKdielectric layer 304 b dielectric causes the upper ELK layer 304 b tohave a lower density and a higher porosity than the lower ELK dielectriclayer 304 a. In some embodiments, the lower and upper ELK dielectriclayers, 304 a and 304 b, are deposited by way of a deposition process(e.g., a physical vapor deposition (PVD) process, a chemical vapordeposition (CVD) process, etc.) performed in a processing chamber heldunder vacuum.

FIG. 8 illustrates some embodiments of a cross-sectional view 800corresponding to act 506. As shown in cross-sectional view 800, a firstcapping layer 308 is deposited over the ELK dielectric layer 304. Thefirst capping layer 308 may be deposited by way of deposition process(e.g., a physical vapor deposition process such as sputtering) performedin a processing chamber held under vacuum.

In some embodiments, the first capping layer 308 may comprise a non-ELKfilm. For example, in some embodiments, the first capping layer 308 maycomprise a silicon nitride (SiN) film having a density of greater than2.4 g/cm³. In other embodiments, the first capping layer 308 maycomprise a silicon carbide nitride (SiCN) film having a density in arange of between approximately 1.5 g/cm³ to approximately 2.0 g/cm³. Inyet other embodiments, the first capping layer 308 may comprise asilicon dioxide (SiO₂) film having a density of approximately 1.5 g/cm³.

In other embodiments, the first capping layer 308 may comprise an ELKfilm having a density that is greater than a density of the underlyingupper ELK dielectric layer 304. For example, in some embodiments, thefirst capping layer 308 may comprise an ELK film comprising a siliconoxycarbide (SiCO) film having a density in a range of betweenapproximately 1.3 g/cm³ to approximately 1.4 g/cm³. In such embodiments,the density corresponds to a dielectric value in a range of betweenapproximately 2.8 to approximately 3.0. The higher density of the ELKfilm, in relation to the ELK dielectric layer 304, provides the firstcapping layer 308 with a lower porosity than that of the ELK dielectriclayer 304, thereby improving selectively and mitigating diffusionthrough the first capping layer 308.

FIG. 9 illustrates some embodiments of a cross-sectional view 900corresponding to act 508. As shown in cross-sectional view 900, ahardmask 902 is selectively formed over the first capping layer 308. Thehardmask 902 comprises a plurality of openings 904 that expose theunderlying first capping layer 308 at positions corresponding to metallayer structures. In some embodiments, the hardmask 902 is selectivelyformed over the first capping layer 308 by forming a photoresist layer906 over the hardmask 902. The photoresist layer 906 is patterned usinga photolithography process, and then the hardmask 902 is exposed to anetchant 908, which removes the hardmask 902 at the plurality of openings904. In some embodiments, the hardmask 902 may comprise titanium (Ti),aluminum (Al), tantalum (Ta), zirconium (Zr), hafnium (Hf), or somecombination thereof, for example.

FIG. 10 illustrates some embodiments of a cross-sectional view 1000corresponding to act 510. As shown in cross-sectional view 1000, anetchant 1002 is applied then to the substrate to selectively etch thefirst capping layer 308 and the ELK dielectric layer 304 according tothe hardmask 902. The etchant 1002 selectively removes the first cappinglayer 308 and the ELK dielectric layer 304 at the one or more openingsin the hardmask 902, resulting in a plurality of cavities 1004 thatextend vertically through the first capping layer 308 into the ELKdielectric layer 304. In various embodiments, the etchant 1002 maycomprise a wet etchant or a dry etchant.

FIG. 11 illustrates some embodiments of a cross-sectional view 1100corresponding to act 512-514. As shown in cross-sectional views 1100, ametal material 1102 is deposited over the substrate. The metal material1102 fills the plurality of cavities 1004 to form a plurality ofstructures in the metal layer 306. In some embodiments, the metalmaterial 1102 may comprise copper deposited by way of deposition process(e.g., a physical vapor deposition such as sputtering). After the metalmaterial 1102 has been deposited, a chemical mechanical polishing (CMP)process is performed to planarize the substrate along line 1104. Thechemical mechanical polishing process removes the hardmask 902 andexcess metal material 1102 without removing first capping layer 308 fromover ELK dielectric layer 304, resulting in a planar interface havingstructures in the metal layer 306 horizontally interspersed between thefirst capping layer 308.

FIG. 12 illustrates some embodiments of a cross-sectional view 1200corresponding to act 516. As shown in cross-sectional view 1200, asecond capping layer 312 is formed over the substrate at a position overthe metal layer 306. In some embodiments, the second capping layercomprises a cobalt capping layer that is separated from the ELKdielectric layer 304 by the first capping layer 308. The first cappinglayer 308 has a high selectivity, such that the thickness of the cobaltcapping layer is much greater over the metal layer 306 than over thefirst capping layer 308. For example, in some embodiments, the thicknessof the cobalt capping layer over the metal layer 306 is greater than tentimes the thickness of the cobalt capping layer over the first cappinglayer 308.

FIG. 13 illustrates some embodiments of a cross-sectional view 1300corresponding to act 518. As shown in cross-sectional view 1300, asecond etch stop layer 314 is formed over the substrate at a positionover the first capping layer 308 and the second capping layer 312. Thesecond etch stop layer 314 is formed to have a first thickness t₁ overthe first capping layer 308 and a second thickness t₂ over the secondcapping layer 312, wherein the first thickness t₁ is greater than thesecond thickness t₂ (i.e., t₁>t₂).

It will be appreciated that while reference is made throughout thisdocument to exemplary structures in discussing aspects of methodologiesdescribed herein, those methodologies are not to be limited by thecorresponding structures presented. Rather, the methodologies andstructures are to be considered independent of one another and able tostand alone and be practiced without regard to any of the particularaspects depicted in the Figs. Additionally, layers described herein canbe formed in any suitable manner, such as with spin on, sputtering,growth and/or deposition techniques, etc.

Also, equivalent alterations and/or modifications may occur to one ofordinary skill in the art based upon a reading and/or understanding ofthe specification and annexed drawings. The disclosure herein includesall such modifications and alterations and is generally not intended tobe limited thereby. For example, although the figures provided hereinare illustrated and described to have a particular doping type, it willbe appreciated that alternative doping types may be utilized as will beappreciated by one of ordinary skill in the art.

In addition, while a particular feature or aspect may have beendisclosed with respect to one of several implementations, such featureor aspect may be combined with one or more other features and/or aspectsof other implementations as may be desired. Furthermore, to the extentthat the terms “includes”, “having”, “has”, “with”, and/or variantsthereof are used herein, such terms are intended to be inclusive inmeaning—like “comprising.” Also, “exemplary” is merely meant to mean anexample, rather than the best. It is also to be appreciated thatfeatures, layers and/or elements depicted herein are illustrated withparticular dimensions and/or orientations relative to one another forpurposes of simplicity and ease of understanding, and that the actualdimensions and/or orientations may differ from that illustrated herein.

Therefore, the present disclosure relates to a method and apparatus forimproving back-end-of-the-line (BEOL) reliability.

In some embodiments, the present disclosure relates to aback-end-of-the-line (BEOL) layer of an integrated chip. The BEOL layercomprises a low-k dielectric layer disposed over a semiconductorsubstrate and one or more metal layer structures disposed within thelow-k dielectric layer. A first capping layer is located over the low-kdielectric layer at positions between the one or more metal layerstructures, wherein the first capping layer is located along a planarinterface having the one or more metal layers interspersed between thefirst capping layer. A second capping layer is located over the one ormore metal layer structures.

In other embodiments, the present disclosure relates to aback-end-of-the-line (BEOL) layer of an integrated chip. The BEOL layercomprises a first etch stop layer disposed over a semiconductorsubstrate and an extreme low-k (ELK) dielectric layer. The ELKdielectric layer comprises a lower ELK dielectric layer disposed overthe first etch stop layer, and an upper ELK dielectric layer disposedover the lower ELK dielectric layer. One or more metal layer structuresare disposed within the ELK dielectric layer. A first capping layer isdisposed over the ELK dielectric layer at positions between the one ormore metal layer structures. The first capping layer has a densitygreater a density of the upper ELK dielectric layer. A second cappinglayer is disposed over the one or more metal layer structures.

In other embodiments, the present disclosure relates to an integratedchip (IC) processing method. The method comprises forming an extremelow-k (ELK) dielectric layer comprising one or more metal layerstructures over a semiconductor substrate. The method further comprisesforming a first capping layer over the ELK dielectric layer at positionsbetween the one or more metal layer structures, wherein the firstcapping layer has a density that is greater than a density of the ELKdielectric layer. The method further comprises forming a second cappinglayer over the one or more metal layer structures to a thickness that isgreater than a thickness of the second capping layer over the firstcapping layer.

1. A back-end-of-the-line (BEOL) layer of an integrated chip,comprising: a low-k dielectric layer disposed over a semiconductorsubstrate; one or more metal layer structures disposed within the low-kdielectric layer; a first capping layer located over the low-kdielectric layer at positions between the one or more metal layerstructures, wherein the first capping layer is located along a planarinterface having the one or more metal layers interspersed between thefirst capping layer; and a second capping layer located over the one ormore metal layer structures.
 2. The BEOL layer of claim 1, wherein thesecond capping layer comprises cobalt (Co).
 3. The BEOL layer of claim1, wherein a thickness of the second capping layer over the metal layerstructures is greater than ten times a thickness of the second cappinglayer over the first capping layer.
 4. The BEOL layer of claim 1,wherein the first capping layer comprises silicon nitride (SiN), siliconcarbon-nitride (SiCN), or silicon dioxide (SiO₂).
 5. The BEOL layer ofclaim 1, wherein the first capping layer comprises an extreme low-k(ELK) film comprising silicon, carbon, and oxygen, wherein the ELK filmhas a greater density than the low-k dielectric layer.
 6. The BEOL layerof claim 5, wherein the ELK film comprises a dielectric constant havinga value in a range of between approximately 2.8 and approximately 3.0and a density in a range of between approximately 1.3 g/cm³ andapproximately 1.4 g/cm³.
 7. The BEOL layer of claim 1, wherein the low-kdielectric layer comprises: a lower extreme low-k (ELK) dielectriclayer; and an upper ELK dielectric layer disposed between the lower ELKdielectric layer and the first capping layer, wherein the upper ELKdielectric layer has a density less than densities of the lower ELKdielectric layer and the first capping layer.
 8. A back-end-of-the-line(BEOL) layer of an integrated chip, comprising: a first etch stop layerdisposed over a semiconductor substrate; an extreme low-k (ELK)dielectric layer comprising a lower ELK dielectric layer disposed overthe first etch stop layer, and an upper ELK dielectric layer disposedover the lower ELK dielectric layer; one or more metal layer structuresdisposed within the ELK dielectric layer; a first capping layer disposedover the ELK dielectric layer at positions between the one or more metallayer structures and having a density greater a density of the upper ELKdielectric layer; and a second capping layer disposed over the one ormore metal layer structures.
 9. The BEOL layer of claim 8, furthercomprising: a second etch stop layer disposed over the first cappinglayer and the second capping layer, wherein the second etch stop layerhas a first thickness over the first capping layer and a secondthickness over the second capping layer, wherein the first thickness isgreater than the second thickness.
 10. The BEOL layer of claim 8,wherein a thickness of the second capping layer over the one or moremetal layer structures is greater than ten times a thickness of thesecond capping layer over the first capping layer.
 11. The BEOL layer ofclaim 8, wherein the second capping layer comprises cobalt (Co).
 12. TheBEOL layer of claim 8, wherein the first capping layer comprises siliconnitride (SiN), silicon carbon-nitride (SiCN), or silicon dioxide (SiO₂).13. The BEOL layer of claim 8, wherein the first capping layer comprisesan ELK film comprising silicon, carbon, and oxygen.
 14. The BEOL layerof claim 13, wherein the ELK film comprises a dielectric constant havinga value in a range of between approximately 2.8 and approximately 3.0and a density in a range of between approximately 1.3 g/cm³ andapproximately 1.4 g/cm³. 15-20. (canceled)
 21. The BEOL layer of claim1, wherein the one or more metal layer structures extend through thefirst capping layer from a first position vertically below the firstcapping layer to a second position vertically over the first cappinglayer.
 22. The BEOL layer of claim 1, wherein the second capping layerhas a greater thickness over the one or more metal layer structures thanover the first capping layer.
 23. The BEOL layer of claim 1, wherein atop surface of the first capping layer and a bottom surface of thesecond capping layer are disposed along a horizontal plane.
 24. Aback-end-of-the-line (BEOL) layer of an integrated chip, comprising: alow-k dielectric layer disposed over a semiconductor substrate; a firstcapping layer comprising a first material located over the low-kdielectric layer; one or more metal layer structures disposed within thelow-k dielectric layer and extending through the first capping layer sothat the one or more metal layer structures are located between thefirst capping layer; and a second capping layer located over the one ormore metal layer structures comprising a second material different thanthe first material, wherein the second capping layer has a greaterthickness over the one or more metal layer structures than over thefirst capping layer.
 25. The BEOL layer of claim 24, wherein the secondcapping layer is more than ten times thicker over the one or more metallayer structures than over the first capping layer.
 26. The BEOL layerof claim 24, wherein a top surface of the first capping layer and abottom surface of the second capping layer are disposed along ahorizontal plane.